Generator of aerosol of powder in gas



Dec. 3, 1957 P. G. ANDRUS ETAL ,3

GENERATOR OF AEROSOL OF POWDER m GA 2 Sheets-Sheet 1 Original FiledMarch 14, 1955 N M 3 w Q a V: Q5565 wzzaz x wmwmw m m w v P528550 8%?amazon 025581 a Dec. 3, 1957 P. G. ANDRUS ETAL 2,8

GENERATOR 0F AEROSOL OF POWDER IN GAS Original Filed March 14, 1955 2Sheets-Shed 2 United States Patent G GENERATOR OF AEROSOL OF POWDER 1NGAS Paul G. Andrus, Columbus, Earnest Paul Matthews, Alliance, andEugene C. Ricker, Columbus, Ohio, assignors, by mesne assignments, toThe Haloid Company, Rochester, N. Y., a corporation of New York Originalapplication March 14, 1955, Serial No. 511,363. and this applicationApril 29, 1955, Serial No. 9

3 Claims. (Cl. 252--359) This invention relates in general to Xerographyand in Xerography uses the physical phenomena of photoa conductivity andelectrostatic attraction of electrostatically charged bodies to converta light image into a physical image consisting of, for instance, blackpowder on white paper. The xerographic plate consists of a film of aphotoconductive insulating material on a metal backing plate. In use,the plate is given an electrostatic surface charge and then exposed to alight image, which results in an electrostatic image on the platesurface. This electrostatic image, which may be allowed to remain on'theplate or which may be transferred, is developed by allowing it toattract and collect electrically charged particles of powder. The powderimage may then be transferred and fixed to another surface, usually asheet of paper, and the plate may be cleaned for reuse or the powderimage may be allowed to remain on the plate for photographing, viewing,or the like.

The xerographic plate usually consists of a sheet of metal on which afilm of selenium has been deposited uniformly by a vacuum evaporationprocess. Materials other than selenium may be used; sulfur andanthracine are examples, though both are much slower photographicallythan selenium. A material suitable for the film on a Xerographic platemust be a good enough insulator in darkness to retain an electricalcharge on its surface for sufiicient time to permit exposure anddevelopment of the plate before much of the charge has leaked away. Thematerial also must dissipate its charge rapidly when the plate isexposed to light.

When sensitizing the plate, ions are deposited on the surface of theplate by the action of an electric field. Two arrangements have beenfound practical for sensitizing plates: (1) corona discharge to provideboth the ions and the electric field, and (2) a radioactive alphaparticle source to ionize the air, used in conjunction with anelectrical field to move ions to the plate.

The Xerographic plate, once sensitized, may be exposed in any of theways ordinarily used for exposing silver halide photographic materials.After exposure to a light image, the plate bears an electrical image inwhich the most highly charged areas correspond to the areas of leastillumination in the light image, the areas of least charge correspond toareas of greatest illumination in the light image, and those ofintermediate charge correspond to areas of intermediate illumination.This electrical image is developed by bringing into contact with itpowder particles.

Two methods of image development are in use. One is described in WalkupU. S. Patent 2,618,551 and is known as cascade development. In thistechnique, the powder is mixed with a granular material and this twocomponent developer is poured or cascaded over the plate surface. Theother form of development is known til) as powder cloud development, andis described for example in Carlson U. S. Patent 2,221,776. In thistechnique of development, a dispersion of powder particles in gas ispassed to the surface area bearing the electrical image and properlycharged particles are drawn out of the cloud to form a powder depositionin electrical image configuration.

The powder image on a plate or other surface may be convenientlytransferred electrostatically to paper by placing the paper on thepowder image and applying a high potential to the back of the paper.Another technique for the transfer of the image from the plate surfaceis by transferring the powder image to an adhesive coated material, suchas paper or the like.

The powder image may be fixed to the transfer material in one of severalways. Some xerographic powders are composed of a resinous materialpigmented with carbon black. These powders may be fixed by heat fusingor by exposing to solvent vapors. Other powders such as finely dividedcharcoal used in some forms of xerography are fixed by spraying with afixative Or by covering them with a transparent adhesive coated film.

It is an object of this invention to improve upon means and methods forthe development of electrostatic latent images.

It is also an object of this invention to improve upon apparatus for thedevelopment of electrostatic latent images.

It is a further object of this invention to improve the art ofXerography by improving powder cloud generators for powder clouddevelopment.

It is a still further object of this invention to provide new means andmethods for creating aerosols of powder in gas.

Generally in powder cloud creating apparatus there is included a powdersource, means to create a cloud of powder in gas, means to convey thecloud to a surface carrying an electrostatic latent image, and means totreat powder in the cloud before it reaches the plate. Such devices,which include one or a number of the above elements, and which are usedto take powder from a source, whether it be a mound of powder or whetherit be in other shapes or forms, and convert the powder to an aerosol ofpowder in gas is herein, and generally in the art, referred to as apowder cloud generator or as a cloud generator.

An object in the art of xerography, as in any art concerned with imagereproduction, is that of uniformly developing high quality copy. Meansof obtaining this objective while using powder cloud development isthrough the uniform and constant presentation to the electrostaticlatent image on a surface of a powder cloud of fine developer powderparticles uniformly and densely dispersed throughout.

And, it is another object of this invention to improve upon powder cloudgenerators so that a more uniform and more dense dispersion of powderparticles in gas than has heretofore been possible is created.

It is yet another object of this invention to improve upon means andmethods of creating uniform and dense dispersions of particles of powderin gas.

The invention of this application follows a new theory for generatinguniform and dense powder clouds. According to this theory, a tape orbelt of cloth or the like which has been uniformly loaded with powderparticles is passed over an output tube at a uniform rate. Particles areblown from the belt or tape in a controlled air stream, therebyproducing a controlled aerosol of uniformly constant and densedispersions of powder particles.

For a better understanding of this invention, together with otherfurther objects thereof, reference is now had to the followingdescription taken in connection with the 3 accompanying drawings, andthe scope of the invention will be pointed out in the appended claims.

Fig. 1 is a block diagram of elements which generally appear inxerographic cloud creating apparatus for use in developing electrostaticcharge patterns.

Fig. 2 is an isometric drawing of an embodiment of a belt which may beused in powder cloud generator accordingto this invention.

Fig. 3 is a cross section View of an embodiment of a powder cloudgenerator according to this invention.

Referring now with more particularity to the drawings, in Fig. 1 isshown a block diagram of elements which compose cloud creating apparatusfor development of electrostatic latent images. As is indicated in thisdiagram, compressed air is fed from compressor 11 to a powder cloudgenerator 13 through a regulating valve 12, and the output of the powdercloud generator is fed through an aerosol handling block 15 and then tothe development zone 16 whereat electrostatically charged developerparticles are passed for development purposes to a surface carrying anelectrostatic latent image.

The source of compressed air or pressurized gas may be any suitablesource, such as for example, an air pump or like pressure generatingmember or a suitable pressurized gas container. Such containers arereadily available on the commercial market in the form of gas capsulesof carbon dioxide or the like under pressure, in the form of bombs orthe like of gas such as fluoro-chloroalkanes, which are available underthe general family name of Freon. Similarly, a suitable system maycomprise a pump or generating means optionally in combination with apressure chamber whereby fluctuations in pressure may be limited oravoided.

Regulating valve 12 is used to control the rate of flow of gas fromcompressor 11 to powder cloud generator 13 and also to control thepressure of gas supplied to the powder cloud generator. The powder cloudgenerator, which is the next block in this diagram following regulatingvalve 12, is used to create an aerosol of powder particles. It may besupplied with powder in what may be termed the raw or bulk form, that ispowder taken directly from a container and directly supplied in thatform without treatment to a powder cloud generator, or it may besupplied with powder which is first treated or positioned and thenplaced in the generator. The particular powder used is dependent on anumber of factors such as other elements used in the cloud creatingapparatus, the form of xerographic development, the desired quality offinal copy, and the like. A more detailed discussion of powders willappear below.

The aerosol handling block 15 of the diagram appeering in Fig. 1 mayrepresent any number of means and apparatus for imparting anelectrostatic charge to the individual powder particles in the aerosolsupplied from the powder cloud generator or it may represent any numberof mean and apparatus for deagglomerating particles fed in the aerosolfrom the generator. Charging and deagglomeration of particles may beaccomplished by turbulently flowing them through fine capillary tubes.Charging may also be accomplished by passing the aerosol of powderparticles through a corona discharge zone, or the like.

The aerosol is next supplied, as indicated by the block diagram, todevelopment zone 16. Generally, this zone includes a means for expandingthe aerosol, and optionally this may be done by leading the air fromtubes or the like to a larger area Where the aerosol expands, creatingthe cloud or expanded aerosol of developer particles in gas. it is alsofeasible and sometimes desirable to use the par 'icles in aerosol formwithout expansion.

In xerography in order to develop a true copy of the original image, itis generally desirable to develop by depositing particles in oppositionto gravitational pull in that the electrostatic charges on the imagebearing surface truly represent the pattern of the. image projected tothe.

manual techniques.

plate surface, and deposition of particles in opposition togravitational forces prevents production of a distorted reproduction.This may be accomplished by positioning the plate with the image bearingsurface facing downward and creating a cloud beneath it. Particles whichdeposit because of other forces may be removed during the developmentprocess through the use of such techniques as directing slight aircurrents or winds to the plate surface. Such winds or currents should besufficient to remove particles not held in place due to electrostaticforces, but should be limited so that particles electrostatically heldin place are not aifected.

It is to. be understood that many modifications may be made in theapparatus described in connection with the block diagram shown in Fig.1.

For example, a device may be inserted between the powder cloud generatorand the aerosol treating block for purposes of further deagglomeratingclumps of particles fed in the aerosol fed from the powder cloud generator. A device may also be inserted between the powder cloud generatorand the aerosol treating block for purposes of dehumidifying thedeveloper powder particles. Such a device may also be inserted betweenthe aerosol treating block and the development zone block. Thesemodifications have been included herein for purposes. of demonstratingthat the powder cloud creating device shown and described in connectionwith Figure l is for illustrative purposes and is intended to includewithin its scope modifications and equivalents able to accomplish thepurpose of generating a powder cloud for deposition on electric chargepatterns.

Reference is now had to Fig. 2 wherein is shown a detailed drawing of anembodiment of a belt or tape which may be used in powder cloudgenerators according to this invention. As appears in this figure, thebelt or tape 17 stretches between two spools, spool 18 and spool 24).The belt 17 may be loaded or impregnated with xerographic developerpowder particles across its entire width or it may be impregnated orloaded with developer powder particles only across a portion of itswidth. Belts may be impregnated by brushing the powder by hand into oragainst the belt and belts may be impregnated. or loaded by tumblingpowder over the belt material and scrap ing off excess powder with ablade or the like. Another technique for loading a belt is that ofworking the powder into the material using a spatula or pressing thepowder into the material between two surfaces. In the brushingtechnique, the material is placed on a solid support and largequantities of powder are brushed over the material in all directionswith a soft bristled brush. Excess powder is removed by shaking thebelt. These manual techniques for impregnating belts are entirelysatisfactory for some uses. However, for high quality xerographicdevelopment, it is desirable to eliminate the variables and humanelements of error which are present with these This may be accomplishedby using an automatic loading machine in which a uniform aerosol ofpowder particles is directed at the belt material as the belt or tapemoves at a uniform rate of speed through the aerosol. The aerosol ofpowder particles which is directed at the belt material should travel ata low enough velocity so that most of the powder particles in theaerosol deposit on or in the belt material. Also the movement of the gasof the aerosol traveling through the belt should not act to remove theparticles in or on the belt material.

Another important consideration in forming belts for high qualityxerographic reproductions is the belt material itself. The materialshould be uniform throughout. This will assure presentation to theaerosol of a material which is at all points able to hold the sameamount of particles and also a material which presents the sameresistance to the flow of particles in the aerosol. The belt materialmay be any porous material such as cotton, asbestos, wool, velvet, silk,synthetic materials, fibrous materials, and the like. A particularlyvaluable asset of the material used for belt or tape 17 is that of itshaving a high nap. Medium weight cotton flannel, for example, has beenfound to work exceptionally well as a belt 17. Equivalents of cottonflannel, such as cotton tape or bias tape material, have been preparedby rubbing the tapes with a wire brush to bring up a nap or to create auniform roughness on the tape or bias surface, and such equivalents havebeen found to work equally as Well.

In impregnating or loading belts, it has been found that belt materialswill accept powder to a saturation point. Powder carried to the beltmaterial above the saturation point may be shaken loose to furtherassure uniformity in belt loading through belt loading of all areas tothe saturation point. It is to be realized, of course, that belts may beloaded well below the saturation point by passing a tape or belt throughan aerosol at high enough speeds to avoid loading to the saturationpoint or by using a thin aerosol in impregnating the belt material.Using an automatic loading machine, it is possible to saturate the beltmaterial with powder particles by passing the belt through the aerosolone time or a number of times. More load per belt will naturally resultusing the same aerosol when the belt is passed through it at the samerate of speed a greater number of times. However, when belt saturationis reached, powder particles will no longer form as a part of beltmaterial, and although some particles may deposit on areas of the belt,these particles may be removed by shaking the belt or the like.

It is to be realized that belts are used as an integral part of thisinvention. However, it is not intended in this invention to devise newmeans, methods or apparatus for loading or impregnating belts or tapesfor use with this invention. The above techniques and apparatus havebeen suggested for illustrative purposes as means of attaining a beltuniformly loaded or impregnated with xerographic developer powderparticles, and the use of all such belts whether the particulartechnique for making them has been disclosed herein or not, is intendedto be encompassed by this invention.

Reference is now had to Fig. 3 wherein is shown a simple embodiment of apowder cloud generator according to this invention. As in Fig. 2, thebelt is designated 17 and the spools are designated 18 and 29. A housing21 encloses the elements of the powder cloud generator and has projectedthrough it an input tube 22 and an output tube 23. A motor 25 acts onand drives a drive capstan 26 through a drive-belt 27. It is to berealized, of course, that motor 25 may be positioned externally ofhousing 21 and the drive-belt 27 extending from motor 25 to drivecapstan 26 can extend to an extension or the like of capstan 26projecting out of housing 21. it is also to be understood that there isno intention to limit the apparatus of this invention to a particulardriving mechanism, but instead other means of driving or causing uniformmovement of belt 17 generally known to those in the art are intended tobe encompassed by this invention.

Drive wheel 28 is positioned to cause belt 17 to contact drive capstan26. The top surface of drive capstan 26 in this embodiment is roughenedand provides a friction form of drive to belt 17, thereby impartingmotion to the belt. Drive wheel 28 is caused to rotate by the movementof belt 1'7 in contact with its surface. Driving forces of rotatingdrive wheel 28 are supplied through gears 32, through friction clutch 33and through gears 34 to the take-up spool, herein designated spool 18.It should be realized that the gearing mechanism and friction clutchcould be directed to spool 20 and that this mechanism has been connectedto spool 18 in this embodiment only for illustrative purposes. The useof the friction clutch and the gearing mechanism to drive the take-upspool is to cause the take-up spool to wind up as much belt material asis supplied to it following use of belt 17 in creating the powderaerosol. The speed of rotation of the take-up spool will vary, dependingon the amount of belt material already wound up on the spool, and thisvariance is provided for through the friction clutch mechanism. Othermechanisms to accomplish the same purpose are intended to be encompassedby this invention. The freedom of rotation of the supply spool iscontrolled by a friction brake 35 or like mechanism. Control on thesupply spool in this way aids in keeping tension on belt 17 as it movesthrough its path from the supply spool to the take-up spool.

Drive wheel 28 is also positioned to cooperate with guide rod 30 tocause positioning of belt 17 during its travel from the supply spool tothe take-up spool over and in contact with the internal opening ofoutput tube 23. Fitting 31 surrounds this opening and is formed topresent a smooth and uniform surface to belt 17 to allow uniform andsmooth movement of belt 17 over the internal opening of output tube 23.The internal opening of output tube 23 should extend to a point withinhousing 21 which distorts the normal straight line movement of belt 17between guide rod 30 and drive wheel 28 to assure close contact of belt17 with the internal opening of output tube 23. Guide rod 30, it is tobe realized, may be a rod, blade, roller or the like.

The belt generator shown in Fig. 3 is prepared for operation by loadingit with a loaded belt similar to the belt shown in Fig. 2. The loadedbelt is generally all on one spool, as for example, spool 28, but it isto be realized, of course, that it could extend between two spools.Spool 18 should be an empty spool when the entire belt is loaded onspool 20 and should be of such size so that it can accommodate all ofbelt 17. Belt 17 is threaded from spool 20 to spool 18 by beingpositioned between guide rod 30 and housing 21 and then over fitting 31and the internal opening of the output tube 23 and then between drivecapstan 26 and drive wheel 28 from where it goes to spool 18. When motor25 is operating, capstan 26 is caused to rotate, which results inmovement of belt 17 at a uniform rate and also results in movement ofspool 18 to cause take-up of belt 17 as it is fed between capstan 26 anddrive wheel 28.

A regulated supply of gas is supplied through input tube 22 to housing21 and a mixture of particles in gas is emitted through output tube 23.The powder for the mixture of powder in gas is supplied from belt 17which passes over the internal opening of output tube 23. Output tube 23is the only means of escape provided from the housing for the gas fedtherein. Belt 17 passes over the internal opening of output tube 23 andpresents a barrier through which the escaping gas must pass. In passingthrough belt 17, the gas carries with it the powder particles which havebeen and are impregnated into and carried by belt 17. Thus, the aerosolof powder particles is created at the output end of output tube 23.

To assure proper operation of a powder cloud generator according to thisinvention, it is desirable to use a belt wide enough in width toentirely cover and extend beyond the internal opening of output tube 23within housing 21. Using such a belt will prevent the escape of gasaround the belt material, which would cause inefficient powder particleaerosol creation. Generally, when dense clouds of powder particles aredesired, a belt should be used which is loaded over an area wider thanthe area of the width of belt 17 over which the internal opening ofoutput tube 23 extends. Such a belt further assures uniformity indensity of cloud created. All the escaping gas in such an instancepasses through loaded areas of the belt only.

The output tube 23 may take varying shapes and forms. Generally theparticular shape depends upon the partic ular output desired and theparticular use to be made of the output aerosol. For example, the outputtube may be a circular tube or may comprise a number of small tubespositioned to create, in effect, a similar circular outline or otheroutline. It may also take the form of a rectangle, square, or the like.It may also vary throughout its length, as for example, the internalopening may comprise a capillary tube or other tube which feeds into awider zone and then feeds into a number of individual tubes or the like.Dimensions of an output tube which are herein included only forillustrative purposes and are not intended to limit the invention in anyway, comprise a .007 inch by inch rectangular slot type of internalopening in a plate fastened over a block containing a A inch drilledhole leading next into a .046 inch drilled hole. To the .046 inchdiameter circular area any of a number of means of conveying an outputfor use in xerography may be attached. The particular output tube beingdescribed has been used generally with belts which are loadedapproximately /2 inch across their width and a generator using theseelements may be used to develop high quality continuous tone xerographicprints in a total time of one second, and in some instances in lesstime.

Using this generator, it has been found that approximately 4 inches ofbelt are necessary for the development of a 4 x 5 print. To develop sucha print in one second, it is necessary to move the belt at the rate of 4inches of belt per second over the internal opening of output tube 23.For greater speed in development, a faster linear speed for the belt isnecessary, and for longer development time slower linear speeds areused. Generally, al though one second developments are obtainable, threesecond developments have been found to produce slightly higher qualityimages. For a three second development using the specific elementsdescribed above, the free air flow at the output end of output tube 23is approximately 2.24 cubic feet per minute with a pressure withinhousing 21 of 60 p. s. i. The belt used to obtain the specific dataabove was of cotton flannel material. It is to be realized that greateramounts of air flow and lesser amounts of air flow are intended to beencompassed by this invention. The air flows and pressure used in thedata supplied above are taken in connection with feeding the outputaerosol from the output tube to a capillary tube for furtherdeagglomeration and charging before feeding the particles to adevelopment zone. The use of capillary tubes or the like requires highpressures and relatively high air flows in order to create turbulentflow of the particles through the capillary tube, which acts both toscour the internal walls of the tube and thereby keep the tube clean,and also to electrostatieally charge the particles as they pass throughthe tube to development zone. When tubes larger than capillary tubes areused, lower pressures and lower rates of air flow aresufilcient forvaluable aerosol outputs for use in development in the art ofxerography.

From the point of view of composition of the developer particlesimpregnated into the tape or belt of material, prints or pictures may beproduced with charcoal, carbon blacks, or carbonaceous pigments. Underproper conditions, any of a number of various carbon or black materialsmay be employed, including such material as furnace blacks, channelblacks and the like. In addition, there may be used such material asmilled charcoals and similar materials, or, if desired, finely dividedmaterials having added pigment matter. In the latter category arematerials such as finely divided resins containing pigments or dyes suchas carbonaceous pigments or various coloring pigments and the like,compositions of this type being preferred where the print or pictureultimately is to be made permanent by a fusing process including heat orvapor fusing. Best prints to date have been made using milled woodcharcoal.

A loaded or impregnated belt is presently believed to have powderextending through all areas of thickness of the belt material. The loadaccepted by each belt is dependent on the density of the cloth and theability of the cloth to load with powder particles. By ability of thecloth to load it is intended to include such elements as 8 the efiect ofthe cloths mesh and the cloths nap, whereas the density is intended toinclude the ettect of such elements as the thickness of the cloth.Powder loaded or impregnated to the belt deposits both between thethreads and on threads and between areas of napped material and, on thenapped material. Belt materials, it is presently believed, have asaturation point above which they will accept within themselves no morexerographic developer powder particles. Although powder particles may befed to the belt material and although such particles may occasionallyremain resting on the surface, they are easily removed by simply shakingthe loaded belt. Thus, particles above the saturation point of the beltwill shake loose, whereas those particles below the saturation pointwhich have become part of the belt material will remain adhering to thebelt material.

Particular features of this invention bring about very high qualityxerographic reproductions. In the first instance, it is desirable tohave a uniform belt uniformly loaded with powder particles. Next, it isdesirable to pass the belt over the output tube at a highly uniform rateof speed while maintaining a highly uniform flow of air into and throughthe air-tight housing. When such measures are taken, the powder cloudgenerator of this invention produces very fine high qualityreproductions.

Throughout, much has been said about high quality reproductions, withoutmuch definition or explanation of what has been intended. Quality inxerography has the same qualifications as are found in the art ofphotography. It is desirable to maintain graininess to a point beyondwhich the human eye cannot see. The average grain size of primaryparticles using powder cloud generators according to this invention, forexample, is believed to be about .3 micron.

The subjective considerations which are present in the art ofphotography are also present in the art of xerography. That is, thefinal print must appear pleasing to the eye and must appear true to theeye. These subjective considerations are obtained by reproductions madeusing the powder cloud generator of this invention.

In addition to the fine photographic qualities desired in prints, thereare also xerographic characteristics which should be present. Usingpowder particles to develop images means that agglomerates of powderparticles may form and may deposit when developing the print. A goodxerographic development system holds the number of agglomerates to aminimum and also holds the size of the agglomerates to a minimum. Thesize of agglomerates and the frequency of agglomerates using the powdercloud generator of this invention are low in both instances.

In xerography it is also desirable to have complete development.Complete development in xerography is intended to include avoidance ofwhat has become known as the halo efiect and the avoidance of fringingof images. The halo effect is a form of halo around developed areas, andfringing is a form of blurring or extending outward from the true imagearea of developer particles. The powder cloud generator according tothis invention when used in conjunction with the proper developmentsystem is capable of very good, complete development. Sensitometricconsiderations, also enter into xerographic reproductions. The desirablefeatures of the powder cloud generator of this invention aid inproducing response curves in the xerographic process, which results ingood correspondence between the original and the reproduction of theoriginal. The resolution of xerographic prints produced while usingpowder cloud generators according to this invention can reach at leastfifty lines per millimeter, and a brightness acceptance range of 1.6density steps has been achieved.

A further factor which qualitatively defines the output of powder cloudgenerators according to this invention is the output consistency eitherusing the same belt or using different belts of equivalent materials andequivalent powder loads. An examination of a large number of prints madewith generators according to this invention has been made, and only aslight variance between prints was noticed. Consistency in outputthroughout the entire belt and from belt to belt is shown by thisexperiment. Consistency of uniformity of dispersion is also presentthroughout a belt and from belt to belt.

A further advantage of generators according to this invention is thatthey are able to deliver a dense cloud which is highly, finely divided,in a very short time. Also, it is to be realized that generatorsaccording to this invention may be quite compact if it is founddesirable or necessary to place them in small areas. The limit oncompactness or smallness is the size of the two spools. Also it is to berealized that when the powder on a spool is used up, replacement ofspools may be easily made, as for example, through the loosening of Wingnuts or the like, without much time loss in equipment operation.

While the present invention as to its objects and advantages, as hasbeen described herein, has been carried out in specific embodimentsthereof, it is not desired to be limited thereby, but is intended tocover the invention broadly within the spirit and scope of the appendedclaims.

What is claimed is:

l. A generator of an aerosol of powder particles for development ofxerographic images comprising a gas tight housing, an input tube, anoutput tube having an internal opening within the housing and anexternal opening extending outside said housing, said input tube adaptedto supply a flow of gas to said housing from a compressed gas source ata sufiicient pressure to form an aerosol of powder particles at theinternal opening of the output tube, said output tube adapted to feed anaerosol of powder particles from said housing, a porous tape of materialadapted to hold powder particles, releasable to gas fiow through saidtape, positioned within said housing, and means Within said housing toposition a portion of the tape of material over the internal opening ofthe output tube, said input tube being positioned relative to saidoutput tube to feed compressed gas into said housing and then throughthe portion of the tape material over the internal opening of the outputtube and then out said output tube.

2. A generator according to claim 1 in which the porous tape of materialis positioned within said housing on two spools.

3. A generator according to claim 2 including drive means to uniformlymove the tape of material from one spool to the other to continuouslypresent new portions of the tape material over the internal opening ofthe output tube at a uniform rate of speed.

References Cited in the file of this patent UNITED STATES PATENTS906,176 Westrook et al. Dec. 8, 1908 1,294,035 Boland Feb. ll, 19192,057,548 Wallach et al. Oct. 13, 1936 2,210,470 Sterling Aug. 6, 19402,217,247 Burns Oct. 8, 1940 2,242,144 Runton May 13, 1941 2,370,636Carlton Mar. 6, 1945 2,602,417 Medcalf July 8, 1952 2,633,824 Dunn etal. Apr. 7, 1953 2,639,543 Abler May 26, 1953 2,659,670 Copley Nov. 17,1953 2,690,979 Law Oct. 5, 1954 2,705,199 Clark Mar. 29, 1955 2,725,304Landrigan et al Nov. 29, 1955 FOREIGN PATENTS 698,994 Great Britain Oct.28. 1953

1. A GENERATOR OF AN AEROSOL OF POWDER PARTICLES FOR DEVELOPMENT OFXEROGRAPHIC IMAGES COMPRISING A GAS TIGHT HOUSING, AN INPUT TUBE, ANOUTPUT TUBE HAVING AN INTERNAL OPENING WITHIN THE HOUSING AND ANEXTERNAL OPENING EXTENDING OUTSIDE SAID HOUSING, SAID INPUT TUBE ADAPTEDTO SUPPLY A FLOW OF GAS TO SAID HOUSING FROM A COMPRESSED GAS SOURCE ATA SUFFICIENT PRESSURE TO FORM AN AEROSOL OF POWDER PARTICLES AT THEINTERNAL OPENING OF THE OUTPUT TUBE, SAID OUTPUT TUBE ADAPTED TO FEED ANAEROSOL OF POWDER PARTICLES FROM SAID HOUSING, A POROUS TAPE OF MATERIALADAPTED TO HOLD POWDER PARTICLES, RELEASABLE TO GAS FLOW THROUGH SAIDTAPE, POSITIONED WITHIN SAID HOUSING, AND MEANS WITHIN SAID HOUSING TOPOSITION A PORTION OF THE TAPE OF MATERIAL OVER THE INTERNAL OPENING OFTHE OUTPUT TUBE, SAID INPUT TUBE BEING POSITIONED RELATIVE TO SAIDOUTPUT TUBE TO FEED COMPRESSED GAS INTO SAID HOUSING AND THEN THROUGHTHE PORTION OF THE TAPE MATERIAL OVER THE INTERNAL OPENING OF THE OUTPUTTUBE AND THEN OUT SAID OUTPUT TUBE.